The overall objective of these studies is to employ the zebrafish (Danio rerio) model to understand the relative role of multiple cytochrome P450 1 (CYP1) and aldo-keto reductase (AKR) enzymes in chemically dependent oxidative stress and DNA damage during development. Oxidative stress may be a key mechanistic point at which pathways leading to toxicity converge. Xenobiotic metabolizing enzymes may contribute to formation of reactive oxygen species (ROS) by toxic/carcinogenic halogenated and polynuclear aromatic hydrocarbons that are aryl hydrocarbon receptor agonists. These compounds elicit severe defects during development, and recent studies suggest a role for CYP1A in some of those effects via uncoupling of the CYP catalytic cycle, or through formation of metabolites that undergo redox cycling resulting in ROS generation. The hypothesis to be addressed is that the multiple CYP1 gene family members, including CYP1A, CYP1B and the novel CYP1C genes, as well as AKR, are involved in generation of ROS leading to oxidative damage and further effects during development in zebrafish. We will test this hypothesis by evaluating the sources and consequences of ROS generation. In the Specific Aims we will: 1) Evaluate changes in expression of CYP1s and AKRs and ROS generation, in relation to global changes in gene expression, the oxidative stress response and DNA damage in embryos exposed to tert-butylhydroquinone or the protoxicants (2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo[a]pyrene). 2) Establish the temporal and cellular patterns of expression of CYP1 A, CYP1B and novel zebrafish CYP1C and AKR genes and their regulation by chemicals during development. 3) Determine the roles of cloned and heterologously expressed zebrafish CYP and AKR in generation of ROS. 4) Establish that CYP1s and AKR contribute significantly to ROSformation in intact cells. 5) Employ morpholino technology to knock down the expression of the CYP1A, CYP1B, CYP1C and AKR genes in embryos, and determine the effect of gene elimination on toxicant-induced formation of ROS in vivo. Knock-down fish will be examined for a) ROS formation, b) altered gene expression measured with microarrays and by PCR analysis of expression of targeted selected genes including a novel zebrafish retrotransposon potentially regulated by oxidative stress, and c) the occurrence of DNA damage.